A laser for WDM must be manufactured exactly the wavelength of which falls within 2 to 3 nm of the expected design clearance. However, since it is difficult to implement the epitaxial growth and the process thereof, the laser wavelength is easily distorted contrary to its expectation.
Accordingly, a method for controlling exactly the laser wavelength is required after the device is manufactured. The tunable laser known in the art typically controls the wavelength thereof by applying an electrical field thereto using unstable properties of matter so as to control its intensity continuously.
The next generation laser for WDM the wavelength of which is less than 2 to 3 nm in its variation can be used.
To be used for a WDM communication network in which lasers the emitting wavelengths of which are slightly different are combined together, controlling the wavelength of an individual laser must be simple and the laser wavelength must be stable against the surrounding environment and its oscillation applied thereto.